Schottky diodes and processes for their manufacture are well known. For example, U.S. Pat. Nos. 4,206,540, 4,398,344 and 4,408,216, in the name of Herbert Gould, describe processes for the manufacture of a schottky diode in which a palladium platinum silicide is used for the schottky barrier to a silicon substrate.
An important characteristic of a schottky diode is a low hot reverse leakage current. Thus, leakage reverse current at, for example, 125.degree. C. may exceed about 10 milliamperes per square millimeter of silicon area. A lower hot reverse leakage current would be desirable, for example, 5 milliamperes per square millimeter.
Another important characteristic of a schottky diode is its turn-on voltage, sometimes called its knee voltage. This voltage should be as low as possible. However, the knee voltage is usually increased when the hot reverse leakage current is reduced. It would be desirable to provide a process in which the hot reverse leakage current can be reduced without an excessive increase in knee voltage.
In the manufacture of schottky diodes, a number of mask steps are used, especially to form a guard ring diffusion. The present invention provides a novel process in which the masks are self aligning.